The present invention relates to controls for vehicular master clutches, preferably wet friction clutches, utilized in partially or fully automated mechanical transmission systems. In particular, the present invention relates to an urge-to-move point calibration method/system utilizing an electronic data link.
Partially and fully automated vehicular mechanical transmission systems utilizing automated friction master clutches are known in the art. These systems are typically employed in a vehicle that includes an engine, a multi-speed transmission having an input shaft brake and at least one traction wheel connected to an output of the transmission. At engine idle speeds with the transmission engaged in a low ratio, such as first gear, it is desirable that the engine generate at the flywheel a small amount of torque sufficient to cause slow or creeping movement of the vehicle if the vehicle brakes are not applied. This mode of operation is analogous to conditions experienced by drivers of passenger automobiles equipped with torque converter-type transmissions. The advantages of this xe2x80x9curge-to-movexe2x80x9d feature in an automatic friction master clutch control is that the vehicle will feel and act like a familiar passenger car equipped with an automatic transmission, the vehicle may be maneuvered at slow speeds using the brake pedal only, and vehicle launches will be quicker with less lurch. The amount of flywheel or output torque generated by an engine at idle speed, and transferable by a clutch in the xe2x80x9curge-to-movexe2x80x9d engagement condition, should be sufficient to allow creeping if the brakes are not applied but small enough to allow the clutch to dissipate the heat energy developed when the clutch is slipped due to application of the vehicle brakes.
A key feature of known automated friction clutch controls is their ability to sense and control engine flywheel torque utilizing an electronically controlled engine connected to a serial communication data link, such as a data link conforming to SAE J1939, and to control the engaged position of a master friction clutch. To improve the controllability and response of prior art master clutch control systems, it is known to determine a clutch control parameter, such as a pulse width modulation (PWM) signal, which corresponds to a clutch touch point position, i.e. the point of initial clutch engagement. However, conventional friction clutch control systems are not necessarily configured to determine a clutch control parameter corresponding to the urge-to-move position of the clutch. Moreover, conventional friction clutch control systems for determining the touch point position are typically designed for a specific vehicle platform rendering the control system inflexible and uneconomical for inclusion in other vehicle platforms having different engine, clutch and transmission system components.
The present invention provides an innovative calibration system/method for an automated master friction clutch, such as a wet friction clutch, which utilizes information available on serial communication data links, such as data links conforming to the SAE J1939, to determine the value of a clutch control parameter corresponding to the urge-to-move position of the master friction clutch.
The inventive control system includes an electronic control unit (ECU) that receives torque information from an engine via a serial communication data link and processes the same according to control logic. The ECU communicates with a clutch controller, which is configured to control the engagement of the clutch.
The clutch operating parameter value corresponding to the clutch urge-to-move position is determined by a calibration routine that is executed according to a pre-determined schedule. Upon determination that the vehicle conditions are safe to begin calibration, the control system determines an approximation of the clutch control parameter value by engaging the clutch until a maximum loaded engine torque sensed during the engagement of the clutch minus an unloaded engine torque exceeds an urge-to-move reference torque. Due to the limited system response, the initial engagement of the clutch will likely yield an approximation of the clutch control parameter value higher than the actual control parameter value (clutch over-engaged). The clutch is then returned to the fully disengaged position and a more detailed search is commenced. The detailed search is characterized by re-applying the clutch in at least one pulse, where the pulse comprises applying the clutch to a position corresponding to a clutch control parameter value, pausing a predetermined time to allow the engine and clutch to stabilize, and then releasing the clutch. The cycle of applying and releasing the clutch is continued until a more accurate control parameter value is determined. The control system then verifies the accuracy of the control parameter value and stores this value in computer memory.
In order to account for inaccuracies in engine torque reporting, the control system subtracts a predetermined offset constant from the verified control parameter value to arrive at a control parameter value that corresponds to the urge-to-move position of the clutch actuator. In most cases the urge-to-move control parameter value is already established from previous operation of the vehicle and stored in computer memory. Due to factors such as clutch wear and temperature changes, the urge-to-move control parameter value can change, and therefore is updated each calibration. The new urge-to-move control parameter value may be used as the updated urge-to-move control parameter value, or a blend of the stored and the new values may be used to determine the updated urge-to-move control parameter value.
The calibration system/method advantageously compensates for variations in system components across multiple vehicle platforms to determine a clutch control parameter value corresponding to the urge-to-move position of the clutch. Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.